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GL1500 Stumble and rough idle

9K views 10 replies 8 participants last post by  jamhow 
#1 ·
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I just joined a day or two ago and have been looking for threads that deal with my problem and wow their are a lot of them, but I can't find just the right one. I have a 1991 Aspencade, 85,000 miles. I have owned it 53,000 of those miles with no real problems. Now it is beginning to idle rough, like it is not hitting on all 6. It has even died a few times at idle. It smooths out around 1500-2000 rpm and runs perfectly.

I changed the plugs tonight. The old ones (I never changed them before) looked great. No excessive wear and a nice tan color. All were about the same. After the change, no difference. But I did notice than the spark looked very weak-- a lot of yellow and not much deep blue. I randomly checked different wires and got the same result with the weak spark. I pulled the wires from various plugs on idle and every one impacted the idle.

I understand that my problem could be caused by anything from dirty filter, dirty carb to bad coils (how do I test those). But I don't think that it is bad wires (I have ridden in some horrific rains recently with no negative impact on performance). I have run some chevron techron in the fuel. But the weak looking spark is making me think electrical.

How about the battery? It starts just fine, (except it won't start until I unpress the starter button) but if the battery is not 100% could that be my problem. Any diffinative voltage tests that would get me anywhere? If I hooked a charged battery up to it with jumper cables while it was running, would that tell me anything?

One other thing, I noticed that I had quite a bit of oil around my alternator. Is that normal on these bikes? I have never seen it drip, but there is oily dirt all the way to the bottom of the motor below the alternator.
 
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#2 ·
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I'm not sure if a old battery will cause this BUT I did replace mine a few months ago and it reall made a diferance in the crancking and how easy it starts now...before it was always tempermental starting, now startss first time everytime hot or cold
 
#3 ·
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Hello & welcome to the forum! From what you describe, it sounds like your low speed circut in 1 or both your carbs is beginning to plug up. You can try a heavy dose of sea foam in the fuel to scrub them out. You can also use the handle of a screw driver & tap the float bowls to help dislodge any crap that might be stuck in your carbs small passages.

Check your air cleaner while your wrenching on it as well!
 
#4 ·
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Hi Jam,
welcome to the forum, I´m not posting because I can help, no cause I have the same Problem. My Wing, also 91 also 85kmls, is not runnimg smooth at idle yet either.
I synched the carbs yesterday, was a bit off and now she runs better. I´ll probably take the carbs out and but them in a bath, should help.
Let´s see who get´s done first...:action:
 
#5 ·
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1500s have several vacuum hoses connected to the carbs and they begin to deteriorate after several years. I suspect that is where you will find the problem. The weak spark is probably because of low charging voltage. With 85,000 miles the alternator is probably getting weak.
 
#7 ·
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jamhow wrote:
Any ideas on what kind of voltages would be acceptable for smooth running at idle?
Not an expert with all this,,,,, but I know you want something over 12 volts up to 13.5 or so.

The oil you mentioned all over the alt. could be a seal behind the alt. I don't know the proper name/terms,,,,,,,,, but if you were to remove the alt. , it slides out of a fin type of thingy (I know there is a better termonology) and I beleive there is a seal in there.

Just a thought,,,,,,,,, there should be a Guru showing up to clarify my description:)
 
#9 ·
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hi jam if it smoothes out at 1500ect thats when the main jet kicks in so you would have an idle jet blockage go with the seafoam for a few tanks and twist the idle screw up and down a few times as for the ault at 85,000 its due an over haul brushes geting low ect and the O ring for the oil
 
#10 ·
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Jamhow, I have the same problem with my 89 gl1500.Idles rough,and stumbles when taking off from a stop until about 2000rpm ,then it smooth's out and runs like a dream.I have rebuilt both carbs ,checked all of the hoses,sync'ed the carbs ,still the same.I was reading the manual and I'm thinking it might be the carb control unit.The carb control unit has a vacuum hose going to it from the right cylinder head .I removed the line from the unit and hooked a hand vacuum pump to the unit ,and at 0-7 " vacuum it runs great , but if you put more than 7 " vacuum on it the bike starts idling rough and stumbles again.Well my bike has around 16" vacuum at idle.Don't know how to check the unit itself.Any idea's?
 
#11 ·
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No I don't. Sounds like you might be onto something though. I left my service manual at the shop, but I will try to check it out and see what it says.

I replaced the air filter and did the sea foam routine today. Didn't get it all back together yet, but will let you know if that helped.
 
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